The present invention relates generally to a device and method for identifying a container and, more particularly, to a device and method for using the slot of the container as an antenna for remote communications.
It is often necessary to monitor the location and movement of materials within a distribution center or manufacturing facility. One method of tracking the materials is to attach a wireless communication device, such as a radio frequency identification (RFID) transponder or other identification device, to containers that are housing the materials. By way of example, a liquid container, such as a barrel or keg, may include an identification device indicative of the liquid contained inside. A transmission device, such as an interrogation reader or transmitter, having an antenna device, is able to send information remotely through electronic signals. Such transmission device is placed throughout the distribution or manufacturing facility to receive signals transmitted from wireless communication devices. The signals are then passed to a central control system that monitors and records the applicable information. The central control system can also send information to its interrogation readers to send to the transponders for response and/or to be stored in the transponder""s memory.
The information communicated by the containers in the system to the interrogation readers may be used for a number of reasons. For example, a statistical analysis may be made of the materials to maintain accurate inventories, production flow rates, and other production standards. Additionally, the identification devices may include specific information about the materials housed within the containers, including date of manufacture, place of manufacture, type of product within the container, temperature of the container and ambient air, temperature of the contents of the container, and pressure of the container, etc.
The wireless communication device must have an antenna arrangement to communicate information about the containers to the interrogation readers. It is generally known for wireless communication devices to include an antenna. It is often a problem for many wireless communication devices to provide an antenna, especially if the wireless communication device is small or is required to be placed in a contained area. The length of the antenna must be tailored to the specific frequency at which the wireless communication device is designed to operate. For low frequencies in the MHz range or lower, an antenna may have to be several inches long to several feet long. The antenna may have to be several inches long for higher frequencies, to allow successful communication at the desired operating frequency.
Additionally, the antenna must either be packaged inside the wireless communication packaging that houses the wireless communication device, or located external to the wireless communication device. External positioning of the antenna to the wireless communication device provides several other challenges when placing the wireless communication device in a confined area, such as in a container. The antenna may have additional problems radiating energy effectively if the antenna is contained internal to a device, such as a container.
Some containers have a natural slot as a characteristic of their manufacture. A slot may be formed by edges of a conductive material coming together in close proximity forming a gap of air between the edges. A slot may also be formed by cutting out or removing material from a conductive surface to form an open or hollow area of free space or air. A slot could be formed by a curl of a cylinder or other surface to form a rim, whereby a slot is created by the gap between the end of the curl and the surface.
For example, a beer keg is made out of a metal material that has an outer wall with a curled end to form a rim. The keg rim is used for handling and movement of the keg. The curled portion of the rim bends inward towards the outer wall, leaving a small gap between the edge of the rim and outer wall. This small gap forms a slot that extends circularly around the keg, and can be used to provide a slot antenna for the wireless communication device. The wireless communication device can be designed to provide electronic connectivity to the slot when installed, so that the slot can be used to provide the effect of an antenna. Since the slot of the container may be several feet long, using the slot for the antenna may be advantageous for communication at lower frequencies where providing an antenna of sufficient length for communication at the desired frequency is problematic.
Therefore, it is advantageous to use the slot of a container to provide an effective antenna for a wireless communication device. One drawback of using the slot of a container to provide an effective antenna is that the impedance of the slot antenna should be matched to the impedance of the communications electronics, which is typically 50 xcexa9. While this is not a problem to provide in a static environment, the impedance of the slot antenna may change as a function of its environment. Specifically, the temperature or atmospheric conditions may affect the size and shape of the slot as the material forming the slot changes shape in response to the changes in the atmospheric conditions or temperature. Further, as these containers may be subjected to robust physical conditions, the shape of the slot may be deformed by dents or other imperfections introduced to the container by handling. Thus, there remains a need for a technique to allow impedance matching in the face of the changing impedance of the slot antenna.
The present invention includes a wireless communication device using a slot antenna arrangement formed by the slot of a container. A wireless communication device is provided with the container to provide information about the identification or other aspects of the container as it moves through manufacturing, tracking or shipping facilities.
An antenna is provided for the wireless communication device so that it can communicate remotely with a transmitter/receiver. One embodiment of the present invention includes an interrogation reader as the transmitter/receiver. The present invention capitalizes on the phenomenon that exists whereby a slot in a conductive material, such as metal, aluminum, copper, or iron for instance, can be coupled to a wireless communication device""s communications electronics to provide the effect of a pole antenna.
Some containers have, by the nature of their construction, a slot that can be used as a slot antenna. Alternatively, a slot can also be cut out of the container. Using a slot antenna, instead of a pole antenna, provides several advantages. The length of the slot necessary for the wireless communication device to operate at the desired frequency may be more suitable than could be provided by using a pole antenna. This is especially true for lower frequency communications that require longer length antennas. Additionally, the slot does not require that a pole device be placed inside or proximate to the container. Using the slot may also be less expensive than using a pole antenna. Additionally, a pole antenna may extend from the container, exposing it to damage.
In one embodiment, the wireless communication device uses feed lines directly connected to the each edge of the slot.
In another embodiment, the wireless communication device includes feed lines that reactively couple with each edge of the slot.
In another embodiment, a conductive device is placed between the slot to couple the wireless communication device to the slot to provide the slot antenna.
In another embodiment, the wireless communication device is mounted on a nonconductive substrate in the slot. A feed line from the wireless communication device rests on the substrate, such that the feed line reactively couples with the slot to provide the slot antenna.
The operating frequency of the slot is substantially matched to the operating frequency of the wireless communication device to maximize the slot antenna radiation efficiency. A circuit is provided between the slot and the wireless communication device to match the impedance of the slot to the impedance of the wireless communication device.
In an alternative embodiment, shorting posts are provided on the ends of the slot to create a slot with the desired length. The shorting posts are constructed out of a conductive material, such as metal, aluminum, copper or iron for example, and are placed between the slot""s edges to short both sides of the slot together. Examples of conductive materials include, but are not limited to, metal, aluminum, copper, and iron.
Variable impedance matching is provided between the wireless communication device and the slot. The variable impedance matching may take a number of different forms, but four variable impedance matching device embodiments are disclosed herein. The first embodiment comprises placing an approximately V-shaped clip that acts as a variable capacitor in the slot. In particular, as the distance between the arms of the clip closes in response to changes in the shape of the slot, the capacitance increases.
A second variable impedance matching embodiment decreases capacitance as the width of the slot decreases. This is accomplished by placing two parallel plates proximate to one another and perpendicular to the longitudinal axis of the slot. The two plates act as a capacitor. As the shape of the slot changes, the plates move from a first position, substantially overlapping, to a non-overlapping second position. This movement reduces the capacitance between the plates.
A third variable impedance matching embodiment increases the inductance as the width of the slot decreases. This is accomplished by placing a helical coil parallel to the lateral axis of the slot. As the slot compresses, the coil compresses such that the inductance increases.
A fourth variable impedance matching embodiment flips the coil such that it is perpendicular to both the lateral and longitudinal axes of the slot. As the width of the slot decreases, the inductance of the coil decreases.
These embodiments allow for a number of different variations to be made so that impedance matching may be effectuated as needed.
The invention also includes a method of monitoring the container. While the container is within a facility, such as during manufacturing, filling, or storing, the container is moved through at least one interrogation point containing an interrogation reader. Communication between the wireless communication device and the interrogation reader is established for monitoring the location and/or content information about the container. A central control system may be in communication with the interrogation point for monitoring the movement of the container. The central control system may monitor the position of the container, or it may monitor specific information that is stored within memory in the device, or both.